The
dpy-20 Gene Suppresses Expression of tba-l(alPha-1) Tubulin Gene in a set of Ventral Cord Excitatory Motor Neurons in C. elegans. T. Fukushige* and S. S. Siddiqui. Lab. of Molecular Biology, Toyohashi University of Technology, Toyohashi 441, Japan. *Present address: Dept of Medical Biochemistry. University of Calgary Medical School, Calgary, Alberta, Canada DNA transformation is a widely used technique in C. elegans, but little is known about the effect of cotransformation markers on the pattern of gene expression in transgenic animals. We have examined the effect of cotransformation markers
dpy-20 and
rol-6 on the expression of tba-l::lacZ alpha-1 tubulin fusion gene in germline transformants. Cellular specificity of the fusion gene expression was found to be very different, depending on the cotransformation marker used. In case of the
rol-6, the tubulin fusion gene expressed in neurons in the head and tail ganglia and a set of 38-39 excitatory motor neurons in the ventral cord along the body length of the animal, which we have identified as the set of DA, DB, VA, and VB neurons. In contrast, for the
dpy-20 marker system, not only fewer neurons were stained in the head and tail ganglia, but the staining of motor neurons in the ventral cord was dramatically reduced both in their number and intensity. This down regulation of the fusion gene expression in motor neurons was observed, irrespective of the orientation of the
dpy-20 chromosomal arrays whether in cis or trans. The
dpy-20 arrays in trans configuration to the
rol-6 and and tba-l::lacZ tubulin fusion gene arrays in the
dpy-20(
e2017) background was obtained as follows. Males from a
dpy-20(
e2017) transgenic culture, carrying the
dpy-20 marker in extra-chromosomal arrays (phenotypically Wild Type), were mated with hermaphrodites carrying the tba-l::lacZ/rol-6 arrays (phenotypically Rollers). In the crossed progeny, many roller lines were selected and individually cloned to produce progeny. Among these, transgenic lines were identified that segregated rollers and dumpy animals (in a non-Mendelian ratio), suggesting that these lines carried the d*Y-20 and the
rol-6 extrachromosomal arrays in the
dpy-20(
e2017) mutant background. Since these lines segregated roller and dumpy progeny independent of each other, clearly the two arrays (
dpy-20 and
rol-6) were not integrated in one extrachromosomal array in these animals. Histochemical staining of these animals revealed that
dpy-20 marker suppressed the alpha tubulin fusion gene expresion in both the cis and trans orientations. In controls, where no cotransformation marker was used, the fusion gene expression closely resembled that of the
rol-6 marker system. Similar suppression results were observed when the
tba-2::lacZ alpha-2 tubulin fusion gene was used in the two systems. Whether the observed suppression is caused by an overexpression of the
dpy-20 gene product, or due to the presence of a DNA sequence (e.g. in the promoter region of the
dpy-20 gene) that inhibits the alpha tubulin expression in motor neurons (such as by titrating a specific transcription factor), remains to be seen. We thank D. Suleman, D. Baillie, J. Kramer. H. Yasuda, and A. Fire for gene markers and suggestions.